1. Technical Field
The present invention relates to biotips.
2. Related Art
Along with the recent development of the techniques that make use of genes, there is growing interest in remedies that use genes, such as in gene diagnosis and gene therapy. Many techniques that use genes for variety discrimination and breeding also have been developed in the field of agriculture and livestock. One widely used technique that makes use of genes is the nucleic acid amplification technique, as represented by PCR (Polymerase Chain Reaction). PCR has become a technique indispensable for understanding the information of biological substances.
PCR generally uses a technique in which a biochemical reaction chamber called a tube or a tip (hereinafter, “biotip”) is used to perform the reaction. However, the techniques of related art are problematic, because the reaction uses large amounts of reagents and other materials, and complex apparatuses to realize the thermal cycle necessary for the reaction. Another problem is that the reaction is time consuming. Accordingly, a biotip or a reactor capable of accurately performing PCR in a short time period using minute amounts of reagents and specimens is needed.
As a countermeasure against these problems, JP-A-2009-136250 discloses a biotip and an apparatus used to perform a thermal cycle reaction by the reciprocal movement of a reaction mixture droplet in a tube filled with a liquid (such as a mineral oil) immiscible with the reaction mixture and having a different specific gravity from that of the reaction mixture.
However, when the biotip disclosed in JP-A-2009-136250 is used for applications where the amplification product is detected by fluorescence measurement performed outside of the chamber, the chamber needs to be made of a transparent material. Resin and heat-resistance glass are among the examples of the transparent material. These materials, however, are easily charged under the influence of, for example, friction. Such charging can be suppressed by subjecting the inner surface of the chamber to a hydrophilic treatment. However, because the reaction mixture is an aqueous solution and adheres to the chamber, the movement of the reaction mixture is impeded. This has made it difficult to employ the hydrophilic treatment for the biotip.
Considering stability against heat and the reaction mixture, a silicone oil or a mineral oil can be used as the liquid immiscible with the reaction mixture and having a different specific gravity from that of the reaction mixture. However, because these oils are generally insulants, the reaction mixture droplet introduced into the oil easily polarizes. For this reason, introducing the reaction mixture into a transparent chamber filled with the oil generates an electric field between the reaction mixture and the chamber. The electric field may cause the reaction mixture to be attracted and adhere to the inner wall of the chamber, or suspended in the oil by repulsion. If PCR is performed under such conditions using a method that moves the reaction mixture in the biotip under the force of gravity (hereinafter, this method will be referred to as “droplet-shuttle” method), the reaction mixture may not move appropriately, and thermal cycling may not be performed desirably.